A preferred field of application for the invention is in brushless DC motors and other permanent magnet motors that can be configured as inner rotor motors or as outer rotor motors. However, the invention can also be applied to other types of electric machines. Electric machines having an inner rotor configuration comprise a rotor arrangement that is mounted onto a shaft and carries one or more permanent magnets, as well as a stator arrangement usually constructed from a number of stacked metal laminations which form a closed stator back yoke from which stator teeth project radially inwards. The stator teeth carry the phase windings. Building up the stator from a stack or packet of laminations has the aim of reducing the eddy current loss in the stator body. The pole shoe serves to absorb the magnetic flux of the stator teeth, stator slots being located between the stator teeth to receive the windings. The rotor arrangement is inserted coaxially into the stator arrangement. In the case of an outer rotor motor, the stator is designed with a back yoke ring and stator teeth projecting radially outwards, the rotor arrangement coaxially enclosing the stator. The stator, consisting of a lamination stack and windings, is often referred to as an armature for both inner rotor motors as well as outer rotor motors.
It is known in the prior art to build up a stator body from a plurality of slotted metal laminations that are die-cut in a shape which corresponds to the cross-section of the stator body and are assembled to form a laminated sheet metal stack. These kinds of laminated stacks make it possible to reduce eddy current loss.
A preferred field of application for the stator arrangement according to the invention is in spindle motors for hard disk drives that contain magnetic or optic storage disks. Such hard disk drives are used in computers, mobile telephones, MP3 players, digital cameras, DVD players and other electronic equipment used to save digital information. These drives are becoming increasingly miniaturized with storage disks having form factors of 2.5 inches, 1.8 inches, 1 inch and 0.85 inches being already included in the prior art, making it thus necessary for the motors to be correspondingly small.
For this field of application, the overall height of the motor, including the winding heads, must consequently be kept as low as possible. Overall motor heights in the magnitude of less than 4 mm are commonplace nowadays.
A stator arrangement for an electric motor is known from JP 2001119871 in which the metal laminations forming the stator arrangement are miniaturized in order to produce a compact spindle motor. In addition to stator teeth, one of the laminations from which the stator is constructed has tongues that are longer than the overall thickness of the lamination stack, the tongues being formed between adjacent stator teeth and bent at a right angle so that they extend along the inside of the back yoke ring and project upwards from the side of the back yoke ring. The projecting part of these tongues at the tip forms a holding element to guide the winding wire between adjacent stator teeth.
One of the problems arising for miniaturized spindle motors is that due to the low permissible overall height of the motor, both the winding space and the space available for the winding terminal is restricted. In the Japanese publication discussed above, the problem also occurs that the tongues extend through the stator slots and, therefore, occupy part of the winding space; due to the small overall volume of the motor, this can result in a noticeable reduction of motor power.
It is an object of the present invention to provide a stator arrangement for an electric machine which is suitable for use in miniaturized hard disk drives. At the same time, the problems concerning the restricted space for the windings and for guiding the winding wires between adjacent stator teeth are to be solved.